1. Field of the Invention
The present invention relates to a magnetic head unit for writing information in and reading information from both sides of a disk shaped magnetic recording medium and a method of manufacturing such a magnetic head unit.
2. Description of the Prior Art
Two-sided recording type disk driving devices for writing information in and reading information from both sides of a disk-shaped magnetic recording medium (hereinafter referred to simply as "disk") are classified by the configuration of the magnatic head supported by a gimbal spring or gimbal springs into three categories, namely, a movable upside/fixed downside system providing a gimbal spring only on a holding case, a fixed upside/movable downside system providing a gimbal spring only on a carriage, and a movable upside/movable downside system providing gimbal springs on both the holding case and the carriage.
In the movable upside/fixed downside system, since the carriage supporting the lower magnetic head is guided directly by a guide bar, the reference plane can be easily established, and hence this system has been widely used. On the other hand, in the fixed upside/movable downside system, since the holding case is supported pivotally on the carriage, the fixed upside/movable downside system has difficulty in establishing the reference plane. Although the movable upside/movable downside system is capable of satisfactory performance, it presents difficulties greater than that of the fixed upside/movable downside system in establishing the reference plane, and hence, in practical application, the movable upside/movable downside system is substantially the movable upside/semi-fixed downside system in which the motion of the gimbal spring provided on the carriage is restricted.
As compared with the movable upside/fixed downside system, the fixed upside/movable downside system has greater difficulty in establishing the reference plane, whereas the following performance of the fixed upside/movable downside system is satisfactory. Accordingly, future development of the fixed upside/movable downside system is desirable. In the movable upside/fixed downside system, the upper holding case has two movable parts, namely, a joint of the holding case and the carriage, and the gimbal spring. Therefore, the following performance of the system is deteriorated in the secondary delay in the following action of those two parts in following the irregularity in the disk. On the contrary, in the fixed upside/movable downside system, the position of the upper magnetic head varies scarcely and the gimbal spring is the only movable part of the lower magnetic head, and hence secondary delay does not occur in the following performance and the fixed upside/movable downside system is advantageous in respect of following performance. Japanese Unexamined Patent Publication No. 57-147160 discloses an invention made in view of such an advantage of the fixed upside/movable downside system. This known invention will be described hereinafter with reference to FIG. 2.
A magnetic head supporting mechanism shown in FIG. 2 is constituted mainly of an arm (holding case) 34 mounted with a magnetic head 32 and a carriage 36 mounted with a magnetic head 33. The arm 34 is connected swingably to the carriage 36 by means of a hinge 35 projecting from the side wall 36a of the carriage 36. The hinge 35 is a spring plate. A predetermined pressure is applied to the arm 34 with a coil spring 37 compressively provided between the arm 34 and the upper wall 36b of the carriage 36. The upper magnetic head 32 is fixed directly to the underside of the arm 34, while the lower magnetic head 33 is attached to the upper surface of the carriage 36 by means of a gimbal plate 38 so that the upper magnetic head 32 and the lower magnetic head 33 are disposed opposite to each other with a disk (flexible disk) 31 therebetween. A supporting spring plate 41 provided with a pivot 40 at the free end thereof is provided with a through hole 39 formed in the lower wall 36c of the carriage 36 below the gimbal plate 38, to press the gimbal plate 38 upward against the disk 31.
The application of the present application proposed an invention, with the same purpose as that of the above-mentioned prior invention, to enable further accurate establishment of a reference plate for the magnetic head mounted on the arm 34. This previous invention will be described hereunder with reference to FIG. 3.
As illustrated in FIG. 3, a magnetic head unit 1 is constituted mainly of a lower magnetic head assembly 40 and an upper magnetic head assembly 30. The magnetic head unit is moved by a pulse motor, not shown, along a guide shaft 4 in the radial direction of a disk 5.
The lower magnetic head assembly 40 comprises a carriage 2, a lower magnetic head 7 mounted through a gimbal spring 6 to the extremity of the carriage 2, a flexible printed wiring board 9 connected to the lower magnetic head 7 with lead wires 8, and lead terminals 10 connected to the flexible printed wiring board 9 and projecting from the base end of the carriage 2. The lead terminals 10 are formed by dividing a conductive metallic plate into five divisions which are incorportated integrally into the carriage 2 by insert molding. One end of each lead terminal 10 is extended near to the gimbal spring 6. The molded carriage 2 integrally has a pivot 11 which abuts against the underside of the gimbal spring 6 at a position corresponding to the lower magnetic head 7 to secure the abutment of the lower magnetic head against the disk 5, and a cylindrical supporting surface 12 which abuts directly on a holding case 3 to support the latter.
The upper magnetic head assembly 30 comprises the holding case 3, a fastening plate 16, and a spring leaf hinge 14 which supports the holding case 3 for swing motion relative to the fastening plate 16. An upper magnetic head 13 is positioned opposite the lower magnetic head 7 mounted on the carriage 2 and is fixed to a plate 21 fixed to the holding case 3. A spring 19 is provided compressively between a holding plate 18 and the holding case 3 to press the holding case 3 resiliently toward the carriage 2. The resilient pressure of the spring 19 is adjustable at an optimum value by means of a pressure adjusting screw 20 provided on the holding plate 18.
The spring leaf hinge 14 and the plate 12 of the upper magnetic head assembly 30 are formed, for example, by cutting a single conductive spring plate incorporated into the holding case 3 by insert molding in a predetermined shape. The plate 21 has a nonelastic construction. One end of the spring leaf hinge 14 is positioned adjacent to the plate 21. The spring leaf hinge 14 is divided, for example, into five divisions to use the spring leaf hinge 14 also as lead terminals. Five lead wires 22 extending from the upper magnetic head 13 are fixed adhesively to the plate 21 and respectively connected to the ends of the five divisions of the spring leaf hinge 14. Of the five lead wires 22, three lead wires are used for reading/writing and two lead wires are used for erasing.
Part of the holding case 3 is projected alongside the flexible portion 14a of the spring leaf hinge 14 to form seats 3a which rest on the cylindrical supporting surface 12. Thus the holding case 3 is swingable around the cylindrical supporting surface 12. Thus, the holding case 3 is positioned stablely by three points of abutment including the two points of abutment of the seats 3a and the cylindrical supporting surface 12 and one point of abutment of the upper magnetic head 13 and the lower magnetic head 6. A holding plate 17a is fixed to the upper surface of the fastening plate 16 with a screw 17 so as to extend over the seats 3a in order to inhibit the upward dislocation of the holding case 3 due to external vibrations or shocks so that the magnetic heads 7 and 13 will not be damaged. Shielding plates 23 and 24 are attached to a portion of the carriage 2 mounted with the lower magnetic head 7 and to a portion of the holding case 3 mounted with the upper magnetic head 13 so as to cover the lower magnetic head 7 and the upper magnetic head 13, respectively, to protect the magnetic heads 7 and 13 from noise.
In attaching the upper magnetic head 13 to the holding case 3, first, the holding case 3 is held in alignment with a reference plane, then the height and the parallelism of the upper magnetic head 13 with respect to the reference plane is adjusted minutely under a microscope by adjusting the position off a chuck holding the upper magnetic head 13, then the upper magnetic head 13 is temporarily fixed to the holding case 3 by a quick hardening adhesive at a predetermined height and parallelism, and then an adhesive is put into the gap between the underside of the upper magnetic head 13 and the holding case 3 to fix the upper magnetic head adhesively to the holding case 3.
Such a fixing method is effective for conventional disk driving apparatus which require adjustment of height and parallelism of the sliding surface of the upper magnetic head for individual upper magnetic head assemblies. However, such a fixing method takes a long time for adjustment and increases assembly costs. Fixed upside/movable downside systems require adjustment of azimuth but only of height and parallelism of the upper magnetic head. Accordingly, there is a need for a method of attaching the upper magnetic head 13 to the holding case without using a microscope and adjusting means having a high degree of freedom of motion.